It is expected that future wireless communication systems will provide broadband services such as wireless Internet access to subscribers. Such broadband services require reliable and high throughput transmissions over a wireless channel which is time dispersive and frequency selective. The wireless channel is subject to limited spectrum and inter-symbol interference (ISI) caused by multipath fading. Orthogonal frequency division multiplexing (OFDM) and OFDMA are some of the most promising solutions for next generation wireless communication systems.
OFDM has a high spectral efficiency since the subcarriers used in the OFDM system overlap in frequency and an adaptive modulation and coding scheme (MCS) may be employed across subcarriers. In addition, implementation of OFDM is very simple because the baseband modulation and demodulation are performed by simple inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) operations. Other advantages of the OFDM system include a simplified receiver structure and excellent robustness in a multipath environment.
OFDM and OFDMA have been adopted by several wireless/wired communication standards, such as digital audio broadcast (DAB), digital audio broadcast terrestrial (DAB-T), IEEE 802.11a/g, IEEE 802.16, asymmetric digital subscriber line (ADSL) and is being considered for adoption in third generation partnership project (3GPP) long term evolution (LTE), cdma2000 evolution, a fourth generation (4G) wireless communication system, IEEE 802.11n, or the like.
One key problem with OFDM and OFDMA is that it is difficult to mitigate or control inter-cell interference to achieve a frequency reuse factor of one. Frequency hopping and subcarrier allocation cooperation between cells have been proposed to mitigate inter-cell interference. However, the effectiveness of both methods is limited.